8. Insect biogeography and evolution

The insects have had a long history since the divergence of the Hexapoda from the Crustacea many millions of years ago. In this time the Earth has undergone much evolution itself, from droughts to floods, from ice ages to arid heat. Extra-terrestrial objects have collided with the Earth, and major extinction events have occurred periodically. Through this long time insects have changed their ranges, and evolved to display the enormous modern diversity outlined in our opening chapter.

In this chapter we review patterns and causes for the distribution of insects on the planet — their biogeography — then introduce fossil and contemporary evidence for their age. We ask what evidence there is for aquatic or terrestrial origins of the group, then address in detail some aspects of insect evolution that have been proposed to explain their success — the origin of wings (and hence flight) and of metamorphosis. We summarize explanations for their diversification and conclude with a review of insects on Pacific islands, highlighting the role of patterns seen there as a more general explanation of insect radiations.